The present invention relates generally to a disc unit, and more particularly to a vibration proof mechanism for use with a suspension that supports a head, and a vibration proof disc unit having the suspension. The present invention is suitable, for example, for a magnetic disc unit that realizes high-speed accesses to mass storage capacity for use with a server.
Recent explosively increasing electronic information content has demanded small, low-profile, and fast-access magnetic disc units, such as HDDs, of mass storage or high surface recording density. A typical HDD includes plural discs to be driven by a spindle motor, plural suspensions each mounted with a magnetic head, a head arm or an actuator connected to the suspension to drive them, and means for transmitting a signal to and from the head.
The magnetic head includes a minute head core that records and reproduces signals, and a slider that supports the head core. Each disc is inserted between a pair of suspensions. The head arm is attached to a proximal wide end of the suspension, and the slider is attached to a distal narrow end of the suspension. The suspension has a triangular shape and serves as a flat spring that presses the slider against a disc. A recent suspension has a printed circuit to be connected to the head, and this type of suspension is known as a wireless suspension.
Plural strap-shaped trunk flexible printed circuit boards (“FPC”) and one main FPC are typically used as the above signal transmission means. The trunk FPC is connected to the main FPC and soldered to the printed circuit of the suspension. The trunk FPC transmits a signal to and from the head. The main FPC is connected to the plural trunk FPCs, attached to the head arm, and mounted with a preamp IC that amplifies the signal. The trunk FPC is attached to a side surface of the suspension, while the head is provided on a top surface of the suspension. The printed circuit covers from the top surface to the side surface of the suspension. This is because the suspension that arranges trunk FPC on its top surface would be so thick that the disc unit cannot be thin or cause collisions between the trunk FPC and the disc. In an illustrative example, an interval between the suspension and the disc is 0.4 mm and a thickness of the trunk FPC is about 0.1 mm.
When the disc stops, the slider contacts the disc due to the compression force by the suspension. When the disc rotates, the associative airflow occurs between the slider and the disc and floats the slider from the disc surface (contact start stop (“CSS”)). A balance between the floating force and the compression force spaces the slider from the disc at a certain distance from the disc. The head arm typically swings and moves the magnetic head to a target position on the disc.
Stable recording and reproducing require the suspension to stabilize seeking by eliminating torsional vibration of a head. The torsional vibration would offset a position of a head from a target position on the disc, causing delayed track servo or inaccessibility.
However, the conventional magnetic disc unit cannot disadvantageously reconcile a demand for miniaturization and a demand for fast access using a high-density disc. The trunk FPC strap is as thick as the side surface of the suspension to avoid influence of the airflow. An air gap exists between the trunk FPC and the side surface of the suspension, because the soldering joint between the printed circuit and the trunk FPC juts out from the side surface of the suspension. This air gap causes turbulence with the airflow, vibrating the trunk FPC. The fast access demand increases a rotational speed of the disc by the spindle motor, and enhances the airflow associated with the rotation. The trunk FPC is thus susceptible to the airflow generated by a rotation of the disc when the suspension swings in a direction orthogonal to the trunk FPC, and would be a vibration source of torsional vibration. The trunk FPC excited by the airflow vibrates the suspension, and deteriorates a positional error signal used to position the head to the target position. Further, the increased surface recording density requires higher precision in positioning the head to a target track. According to the inventors' studies, this vibration of the trunk FPC becomes non-negligible when the rotational speed is higher than 10,000 rpm or higher, the capacity becomes about 70 GB or higher so that the surface recording density is higher than 60,000 dpi or higher.